MPLS Working Group I. Busi (Ed)
Internet Draft Alcatel-Lucent
Intended status: Informational
B. Niven-Jenkins (Ed)
BT
Expires: January 2010 July 13, 2009
MPLS-TP OAM Framework
draft-ietf-mpls-tp-oam-framework-01.txt
Status of this Memo
This Internet-Draft is submitted to IETF in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF), its areas, and its working groups. Note that other
groups may also distribute working documents as Internet-Drafts.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress".
The list of current Internet-Drafts can be accessed at
http://www.ietf.org/ietf/1id-abstracts.txt
The list of Internet-Draft Shadow Directories can be accessed at
http://www.ietf.org/shadow.html
Copyright Notice
Copyright (c) 2009 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents in effect on the date of
publication of this document (http://trustee.ietf.org/license-info).
Please review these documents carefully, as they describe your rights
and restrictions with respect to this document.
Busi et al. Expires January 13, 2010 [Page 1]
Internet-Draft MPLS-TP OAM Framework July 2009
Abstract
Multi-Protocol Label Switching (MPLS) Transport Profile (MPLS-TP) is
based on a profile of the MPLS and pseudowire (PW) procedures as
specified in the MPLS Traffic Engineering (MPLS-TE), pseudowire (PW)
and multi-segment PW (MS-PW) architectures complemented with
additional Operations, Administration and Maintenance (OAM)
procedures for fault, performance and protection-switching management
for packet transport applications that do not rely on the presence of
a control plane.
This document provides a framework that supports a comprehensive set
of OAM procedures that fulfills the MPLS-TP OAM requirements [11].
Table of Contents
1. Introduction.................................................3
1.1. Contributing Authors....................................4
2. Conventions used in this document............................4
2.1. Terminology.............................................4
2.2. Definitions.............................................5
3. Functional Components........................................7
3.1. Maintenance Entity......................................9
3.2. Point-to-multipoint scenario............................9
3.3. Maintenance End Points (MEPs)..........................10
3.4. Maintenance Intermediate Points (MIPs).................12
3.5. Server MEPs............................................12
4. Reference Model.............................................13
4.1. MPLS-TP Section Monitoring.............................15
4.2. MPLS-TP LSP End-to-End Monitoring......................16
4.3. MPLS-TP LSP Tandem Connection Monitoring...............17
4.4. MPLS-TP PW Monitoring..................................19
4.5. MPLS-TP MS-PW Tandem Connection Monitoring.............19
5. OAM Functions for pro-active monitoring.....................21
5.1. Continuity Check and Connectivity Verification.........21
5.1.1. Defects identified by CC-V........................22
5.1.1.1. Loss Of Continuity defect....................22
5.1.1.2. Mis-connectivity defect......................22
5.1.1.3. MEP misconfiguration defect..................23
5.1.1.4. Period Misconfiguration defect...............23
5.1.2. Consequent action.................................23
5.1.3. Configuration considerations......................24
5.1.4. Applications for proactive CC-V...................25
5.2. Remote Defect Indication...............................26
5.2.1. Configuration considerations......................26
5.2.2. Applications for Remote Defect Indication.........26
5.3. Alarm Reporting........................................27
Busi et al. Expires January 13, 2010 [Page 2]
Internet-Draft MPLS-TP OAM Framework July 2009
5.4. Lock Reporting.........................................28
5.5. Lock Indication........................................29
5.6. Packet Loss............................................29
5.6.1. Configuration considerations......................29
5.6.2. Applications for Packet Loss......................30
5.7. Client Failure Indication..............................30
5.7.1. Configuration considerations......................31
5.7.2. Applications for Remote Defect Indication.........31
5.8. Delay Measurement......................................31
5.8.1. Configuration considerations......................32
5.8.2. Applications for Packet Loss......................32
6. OAM Functions for on-demand monitoring......................32
6.1. Connectivity Verification..............................32
6.1.1. Configuration considerations......................33
6.2. Packet Loss............................................34
6.2.1. Configuration considerations......................34
6.2.2. Applications for On-demand Packet Loss............34
6.3. Diagnostic.............................................34
6.4. Route Tracing..........................................35
6.5. Delay Measurement......................................35
6.5.1. Configuration considerations......................35
6.5.2. Applications for Delay Measurement................35
6.6. Lock Instruct..........................................36
7. Security Considerations.....................................36
8. IANA Considerations.........................................36
9. Acknowledgments.............................................36
10. References.................................................37
10.1. Normative References..................................37
10.2. Informative References................................37
1. Introduction
As noted in [8], MPLS-TP defines a profile of the MPLS-TE and (MS-)PW
architectures defined in RFC 3031 [2], RFC 3985 [5] and [7]
complemented with additional OAM procedures for fault, performance
and protection-switching management for packet transport
applications.
[Editor's note - The draft needs to be reviewed to ensure support of
OAM for p2mp transport paths]
In line with [12], existing MPLS OAM mechanisms will be used wherever
possible and extensions or new OAM mechanisms will be defined only
where existing mechanisms are not sufficient to meet the
requirements.
Busi et al. Expires January 13, 2010 [Page 3]
Internet-Draft MPLS-TP OAM Framework July 2009
The MPLS-TP OAM framework defined in this document provides a
comprehensive set of OAM procedures that satisfy the MPLS-TP OAM
requirements [11]. In this regard, it is similar to existing
SONET/SDH and OTH OAM mechanisms (e.g. [16]).
1.1. Contributing Authors
Italo Busi, Ben Niven-Jenkins, Annamaria Fulignoli, Enrique
Hernandez-Valencia, Lieven Levrau, Dinesh Mohan, Vincenzo Sestito,
Nurit Sprecher, Huub van Helvoort, Martin Vigoureux, Yaacov
Weingarten, Rolf Winter
2. Conventions used in this document
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC-2119 [1].
2.1. Terminology
DBN Domain Border Node
LME LSP Maintenance Entity
LTCME LSP Tandem Connection Maintenance Entity
[Editor's note - Difference or similarity between tandem connection
monitoring (TCM)_and Path Segment Tunnel (PST) need to be defined and
agreed]
ME Maintenance Entity
[Editor's note - There is a need to define whether to support OAM on
p2mp transport path there is a need to introduce the MEG concept]
MEP Maintenance End Point
MIP Maintenance Intermediate Point
PHB Per-hop Behavior
PME PW Maintenance Entity
PTCME PW Tandem Connection Maintenance Entity
SME Section Maintenance Entity
Busi et al. Expires January 13, 2010 [Page 4]
Internet-Draft MPLS-TP OAM Framework July 2009
2.2. Definitions
ME: The collection of MEPs and MIPs and their association (details in
section 3.1).
MEP: A MEP is capable of initiating (MEP Source) and terminating (MEP
Sink) OAM messages for fault management and performance monitoring.
MEPs reside at the boundaries of an ME (details in section 3.3).
MEP Source: A MEP acts as MEP source for the OAM messages that it
originates and inserts into its associated ME.
MEP Sink: A MEP acts as a MEP sink for the OAM messages that it
terminates and processes from its associated ME.
MIP: A MIP terminates and processes OAM messages and generates OAM
messages in reaction to received OAM messages. A MIP resides within a
ME between MEPs (details in section 3.4).
OAM domain: A domain, as defined in [10], whose entities are grouped
for the purpose of keeping the OAM confined within that domain.
Note - within the rest of this document the term "domain" is used to
indicate an "OAM domain"
OAM flow: An OAM flow is a flow of OAM packets between a pair of MEPs
or a MEP and a MIP that is used to monitor and maintain a ME
[Editor's note - a MEG depending on what we decide for this point].
An OAM flow is associated to a unique ME and contains the OAM
monitoring, signalling and notification messages necessary to monitor
and maintain that ME. The exact mix of message types in an OAM flow
will be dependent on the technology being monitored and the exact
deployment scenario of that technology (e.g. some deployments may
proactively monitor the connectivity of all transport paths whereas
other deployments may only reactively monitor transport paths).
OAM Message: An OAM information element that performs some OAM
functionality (e.g. continuity check and connectivity verification)
OAM Packet: A packet that carries one or more OAM messages (i.e. OAM
information elements).
Path: See Transport Path
Signal Fail: A condition when the data associated with a transport
path has failed in the sense that a defect condition (not being a
degraded defect) is detected.
Busi et al. Expires January 13, 2010 [Page 5]
Internet-Draft MPLS-TP OAM Framework July 2009
Tandem Connection: A tandem connection is an arbitrary part of a
transport path that can be monitored (via OAM) independently from the
end-to-end monitoring (OAM). It may be a monitored segment or a
monitored concatenated segment of a transport path. The tandem
connection may also include the forwarding engine(s) of the node(s)
at the edge(s) of the segment or concatenated segment.
The following terms are defined in [10] as follows:
Associated bidirectional path: A path that supports traffic flow in
both directions but which is constructed from a pair of
unidirectional paths (one for each direction) which are associated
with one another at the path's ingress/egress points. The forward
and backward directions are setup, monitored and protected
independently. As a consequence they may or may not follow the same
route (links and nodes) across the network.
Concatenated Segment: A serial-compound link connection as defined in
G.805 [17]. A concatenated segment is a contiguous part of an LSP or
multi-segment PW that comprises a set of segments and their
interconnecting nodes in sequence. See also "Segment".
Co-routed bidirectional path: A path where the forward and backward
directions follow the same route (links and nodes) across the
network. Both directions are setup, monitored and protected as a
single entity. A transport network path is typically co-routed.
Layer network: Layer network is defined in G.805 [17]. A layer
network provides for the transfer of client information and
independent operation of the client OAM. A Layer Network may be
described in a service context as follows: one layer network may
provide a (transport) service to higher client layer network and may,
in turn, be a client to a lower layer network. A layer network is a
logical construction somewhat independent of arrangement or
composition of physical network elements. A particular physical
network element may topologically belong to more than one layer
network, depending on the actions it takes on the encapsulation
associated with the logical layers (e.g. the label stack), and thus
could be modeled as multiple logical elements. A layer network may
consist of one or more sublayers. Section 1.3 provides a more
detailed overview of what constitutes a layer network. For
additional explanation of how layer networks relate to the OSI
concept of layering see Appendix I of Y.2611 [19].
Section Layer Network: A section layer is a server layer (which may
be MPLS-TP or a different technology) which provides for the transfer
of the section layer client information between adjacent nodes in the
Busi et al. Expires January 13, 2010 [Page 6]
Internet-Draft MPLS-TP OAM Framework July 2009
transport path layer or transport service layer. A section layer may
provide for aggregation of multiple MPLS-TP clients. Note that G.805
[17] defines the section layer as one of the two layer networks in a
transmission media layer network. The other layer network is the
physical media layer network.
Path: See Transport Path
Segment: A link connection as defined in G.805 [17]. A segment is the
part of an LSP that traverses a single link or the part of a PW that
traverses a single link (i.e. that connects a pair of adjacent
{Switching|Terminating} Provider Edges). See also "Concatenated
Segment".
Sublayer: Sublayer is defined in G.805 [17]. The distinction between
a layer network and a sublayer is that a sublayer is not directly
accessible to clients outside of its encapsulating layer network and
offers no direct transport service for a higher layer (client)
network
Transport Path Layer: A (sub-)layer network that provides
point-to-point or point-to-multipoint transport paths. It provides
independent (of the client) OAM when transporting its clients.
Unidirectional path: A path that supports traffic flow in only one
direction.
The term 'Domain Border Node' is defined in [14] as follows:
Domain Border Node: To be defined
[Editor's note - There is no definition of Domain Border Node in RFC
5151]
The term 'Per-hop Behavior' is defined in [13] as follows:
Per-hop Behavior: a description of the externally observable
forwarding treatment applied at a differentiated services-compliant
node to a behavior aggregate.
3. Functional Components
MPLS-TP defines a profile of the MPLS and PW architectures ([2], [5]
and [7]) that is designed to transport service traffic complying with
certain performance and quality requirements. In order to verify and
maintain these performance and quality requirements, there is a need
to not only apply OAM functionality on a transport path granularity
Busi et al. Expires January 13, 2010 [Page 7]
Internet-Draft MPLS-TP OAM Framework July 2009
(e.g. LSP or MS-PW), but also on arbitrary parts of transport paths,
defined as Tandem Connections, between any two arbitrary points along
a path.
MPLS-TP OAM operates in the context of Maintenance Entities (MEs).
A Maintenance Entity is the collection of two (or more) Maintenance
End Points (MEPs) and their association. The MEPs that form an ME are
configured and managed to limit the scope of an OAM flow within the
ME the MEPs belong to (i.e. within the domain of the transport path
or segment, in the specific layer network, that is being monitored
and managed).
An example of an ME with more than two MEPs is a point-to-multipoint
ME monitoring a point-to-multipoint transport path (or point-to-
multipoint tandem connection).
Each MEP resides at the boundaries of the ME that they are part of.
An ME may also include a set of zero or more Maintenance Intermediate
Points (MIPs), which reside within the Maintenance Entity, between
the MEPs.
MEPs and MIPs are associated with only one Maintenance Entity.
The abstract reference model for a ME with MEPs and MIPs is described
in Figure 1 below:
+-+ +-+ +-+ +-+
|A|----|B|----|C|----|D|
+-+ +-+ +-+ +-+
Figure 1 ME Abstract Reference Model
The instantiation of this abstract model to different MPLS-TP
entities is described in section 4. In this model, nodes A, B, C and
D can be LER/LSR for an LSP or the {S|T}-PEs for a MS-PW. Nodes A and
D are MEPs while B and C are MIPs. The links connecting adjacent
nodes can be either physical links or lower-level LSPs.
This functional model defines the relationships between all OAM
entities from a maintenance perspective, to allow each Maintenance
Entity to monitor and manage the layer network under its
responsibility and to localize problems efficiently.
Busi et al. Expires January 13, 2010 [Page 8]
Internet-Draft MPLS-TP OAM Framework July 2009
When a control plane is not present, the management plane configures
MEPs and MIPs. Otherwise they can be configured either by the
management plane or by the control plane.
3.1. Maintenance Entity
A Maintenance Entity may be defined to monitor for fault and
performance management unidirectional point-to-point or point-to-
multipoint transport paths or tandem connections, or co-routed
bidirectional point-to-point transport paths and tandem connections
in an MPLS-TP layer network.
In case of associated bi-directional paths, two independent
Maintenance Entities are define to independently monitor each
direction.
An MPLS-TP maintenance entity can be either the whole end-to-end
transport path or a Tandem Connection of the transport path.
The following properties apply to all MPLS-TP MEs:
o They can be nested but not overlapped, e.g. a ME may cover a
segment or a concatenated segment of another ME, and may also
include the forwarding engine(s) of the node(s) at the edge(s) of
the segment or concatenated segment, but all its MEPs and MIPs are
no longer part of the encompassing ME. It is possible that MEPs of
nested MEs reside on a single node.
o Each OAM flow is associated with a single Maintenance Entity.
o OAM packets are subject to the same forwarding treatment (e.g.
fate share) as the data traffic, but they can be distinguished
from the data traffic using the GAL and ACH constructs [9] for LSP
and the ACH construct [6]and [9] for (MS-)PW.
3.2. Point-to-multipoint scenario
The reference model for the p2mp scenario is represented in Figure 4.
Busi et al. Expires January 13, 2010 [Page 9]
Internet-Draft MPLS-TP OAM Framework July 2009
+-+
/--|D|
/ +-+
+-+
/--|C|
+-+ +-+/ +-+\ +-+
|A|----|B| \--|E|
+-+ +-+\ +-+ +-+
\--|F|
+-+
Figure 2 Reference Model for p2mp
In case of p2mp transport paths, the OAM measurements are different
for each [Root, Leaf] relationship (A-D, A-E and A-F):
o Fault conditions - depending from where the failure is located
o Packet loss - depending from where the packets are lost
o Packet delay - depending on different paths
Each leaf (i.e. D, E and F) terminates OAM messages to monitor its
own [Root, Leaf] relationship while the root (i.e. A) generates OAM
messages to monitor all the [Root, Leaf] relationships of p2mp
transport path.
[Editor's note - Further considerations regarding the p2mp case will
be added in a future version of this document]
3.3. Maintenance End Points (MEPs)
Maintenance End Points (MEPs) are the end points of a ME.
In the context of an MPLS-TP LSP, only LERs can be MEPs while in the
context of an LSP Tandem Connection both LERs and LSRs can be MEPs.
In the context of MPLS-TP PW, only T-PEs can be MEPs while in the
context of a PW Tandem Connection both T-PEs and S-PEs can be MIPs.
MEPs are responsible for activating and controlling all of the OAM
functionality for the ME. A MEP is capable of initiating and
terminating OAM messages for fault management and performance
monitoring.
Busi et al. Expires January 13, 2010 [Page 10]
Internet-Draft MPLS-TP OAM Framework July 2009
MEPs prevent OAM packets corresponding to a ME from leaking outside
that ME:
o A MEP sink terminates all the OAM packets that it receives
corresponding to its ME and does not forward them further along
the path. If the pro-active CC-V OAM tool detects an unintended
connectivity, all traffic on the path is blocked (i.e. all
received packets are dropped, including user-data packets).
[Editor's note - Need to discuss whether to keep the last sentence in
the bullet above regarding the MEP behavior in case of
misconnections]
o A MEP source tunnels all the OAM packets that it receives,
upstream from the associated ME, via label stacking. These packets
are not processed within the ME as they belong to another ME.
[Editor's - Need to rephrase the bullet above to clarify what it
actually means]
MPLS-TP MEP passes a fault indication to its client (sub-)layer
network.
A MEP of a tandem connection is not necessarily coincident with the
termination of the MPLS-TP transport path (LSP or PW). Within the
boundary of the tandem connection it can monitor the MPLS-TP
transport path for failures or performance degradation (e.g. count
packets).
[Editor's note - The MEP of a TCM monitors the transport paths'
connectivity within the scope of the TCM. This means that failures or
performance degradations within the TCM are detected by the TCM MEP
while failures or performance degradations outside the TCM are not
detected by the TCM MEP.
Improve the text above to explain this concept.]
A MEP of an MPLS-TP transport path coincides with transport path
termination and monitors it for failures or performance degradation
(e.g. based on packet counts) in an end-to-end scope. Note that both
MEP source and MEP sink coincide with transport paths' source and
sink terminations.
[Editor's note - Add some text regarding MEP identification as well
as about what a MEP should do if it receives an unexpected OAM
packet]
Busi et al. Expires January 13, 2010 [Page 11]
Internet-Draft MPLS-TP OAM Framework July 2009
3.4. Maintenance Intermediate Points (MIPs)
A Maintenance Intermediate Point (MIP) is a point between the two
MEPs in an ME.
In the context of an MPLS-TP LSP and LSP Tandem Connections, LSRs can
be MIPs.
In the context of MPLS-TP PW and PW Tandem Connection, S-PEs can be
MIPs.
A MIP is capable of reacting to some OAM packets and forwarding all
the other OAM packets while ensuring fate sharing with data plane
packets.
A MIP does not initiate unsolicited OAM packets, but may be addressed
by OAM packets initiated by one of the MEPs of the ME. A MIP can
generate OAM packets only in response to OAM packets that are sent on
the ME it belongs to.
[Editor's note - It is needed to provide an high-level description
about how this is achieved (e.g. TTL expiry).]
MIPs are unaware of any OAM flows running between MEPs or between
MEPs and other MIPs. MIPs can only receive and process OAM packets
addressed to the MIP itself.
A MIP takes no action on the MPLS-TP transport path.
[Editor's note - Add some text regarding MIP identification as well
as about what a MIP should do if it receives an unexpected OAM
packet]
3.5. Server MEPs
A server MEP is a MEP of an ME that is either:
o defined in a layer network below the MPLS-TP layer network being
referenced, or
o defined in a sub-layer of the MPLS-TP layer network that is below
the sub-layer being referenced.
A server MEP can coincide with a MIP or a MEP in the client (MPLS-TP)
layer network.
Busi et al. Expires January 13, 2010 [Page 12]
Internet-Draft MPLS-TP OAM Framework July 2009
A server MEP provides also client/server adaptation function between
the client (MPLS-TP) layer network and the server layer network. As a
consequence the server MEP is aware of the MPLS-TP transport paths
that are setup over that server layer's transport path.
For example, a server MEP can be either:
o A termination point of a physical link (e.g. 802.3), an SDH VC or
OTH ODU for the MPLS-TP Section layer network, defined in section
4.1;
o An MPLS-TP Section MEP for MPLS-TP LSPs, defined in section 4.2;
o An MPLS-TP LSP MEP for MPLS-TP PWs, defined in section 4.4;
o An MPLS-TP LSP Tandem Connection MEP for higher-level LTCMEs,
defined in section 4.3;
o An MPLS-TP PW Tandem Connection MEP for higher-level PTCMEs,
defined in section 4.5.
The server MEP can run appropriate OAM functions for fault detection
within the server (sub-)layer network, and notifies a fault
indication to its client MPLS-TP layer network. Server MEP OAM
functions are outside the scope of this document.
4. Reference Model
The reference model for the MPLS-TP framework builds upon the concept
of an ME, and its associated MEPs and MIPs, to support the functional
requirements specified in [11].
The following MPLS-TP MEs are specified in this document:
o A Section Maintenance Entity (SME), allowing monitoring and
management of MPLS-TP Sections (between MPLS LSRs).
o A LSP Maintenance Entity (LME), allowing monitoring and management
of an end-to-end LSP (between LERs).
o A PW Maintenance Entity (PME), allowing monitoring and management
of an end-to-end SS/MS-PWs (between T-PEs).
o An LSP Tandem Connection Maintenance Entity (LTCME), allowing
monitoring and management of an LSP Tandem Connection between any
LER/LSR along the LSP.
Busi et al. Expires January 13, 2010 [Page 13]
Internet-Draft MPLS-TP OAM Framework July 2009
o A MS-PW Tandem Connection Maintenance Entity (PTCME), allows
monitoring and management of a SS/MS-PW Tandem Connection between
any T-PE/S-PE along the (MS-)PW.
The MEs specified in this MPLS-TP framework are compliant with the
architecture framework for MPLS MS-PWs [7] and MPLS LSPs [2].
Hierarchical LSPs are also supported. In this case, each LSP Tunnel
in the hierarchy is a different sub-layer network that can be
monitored independently from higher and lower level LSP tunnels in
the hierarchy, end-to-end (from LER to LER) by an LME. Tandem
Connection monitoring via LTCME are applicable on each LSP Tunnel in
the hierarchy.
Native |<------------------- MS-PW1Z ------------------->| Native
Layer | | Layer
Service | |<-PSN13->| |<-PSN3X->| |<-PSNXZ->| | Service
(AC1) V V LSP V V LSP V V LSP V V (AC2)
+----+ +-+ +----+ +----+ +-+ +----+
+----+ |TPE1| | | |SPE3| |SPEX| | | |TPEZ| +----+
| | | |=========| |=========| |=========| | | |
| CE1|--------|........PW13.......|...PW3X..|........PWXZ.......|-------|CE2 |
| | | |=========| |=========| |=========| | | |
+----+ | 1 | |2| | 3 | | X | |Y| | Z | +----+
+----+ +-+ +----+ +----+ +-+ +----+
. . . .
| | | |
|<---- Domain 1 --->| |<---- Domain Z --->|
.------------------- PW1Z PME -------------------.
.---- PW13 PTCME ---. .---- PWXZ PTCME ---.
.---------. .---------.
PSN13 LME PSNXZ LME
.---. .---. .---------. .---. .---.
Sec12 Sec23 Sec3X SecXY SecYZ
SME SME SME SME SME
TPE1: Terminating Provider Edge 1 SPE2: Switching Provider Edge 3
TPEX: Terminating Provider Edge X SPEZ: Switching Provider Edge Z
.---. ME . MEP ==== LSP .... PW
Figure 3 Reference Model for the MPLS-TP OAM Framework
Busi et al. Expires January 13, 2010 [Page 14]
Internet-Draft MPLS-TP OAM Framework July 2009
Figure 3 depicts a high-level reference model for the MPLS-TP OAM
framework. The figure depicts portions of two MPLS-TP enabled network
domains, Domain 1 and Domain Z. In Domain 1, LSR1 is adjacent to LSR2
via the MPLS Section Sec12 and LSR2 is adjacent to LSR3 via the MPLS
Section Sec23. Similarly, in Domain Z, LSRX is adjacent to LSRY via
the MPLS Section SecXY and LSRY is adjacent to LSRZ via the MPLS
Section SecYZ. In addition, LSR3 is adjacent to LSRX via the MPLS
Section 3X.
Figure 3 also shows a bi-directional MS-PW (PW1Z) between AC1 on TPE1
and AC2 on TPEZ. The MS-PW consists of three bi-directional PW
Segments: 1) PW13 segment between T-PE1 and S-PE3 via the bi-
directional PSN13 LSP, 2) PW3X segment between S-PE3 and S-PEX, and
3) PWXZ segment between S-PEX and T-PEZ via the bi-directional PSNXZ
LSP.
The MPLS-TP OAM procedures that apply to an instance of a given ME
are expected to operate independently from procedures on other
instances of the same ME and certainly of other MEs. Yet, this does
not preclude that multiple MEs may be affected simultaneously by the
same network condition, for example, a fibre cut event.
Note that there are no constrains imposed by this OAM framework on
the number, or type, of MEs that may be instantiated on a particular
node. In particular, when looking at Figure 1, it should be possible
to configure one or more MEPs on the same node if that node is the
endpoint of one or more MEs.
Figure 3 does not describe a PW3X PTCME because typically TCMs are
used to monitor an OAM domain (like PW13 and PWXZ PTCMEs) rather
than the segment between two OAM domains. However the OAM framework
does not pose any constraints on the way TCM are instantiated as long
as they are not overlapping.
The subsections below define the MEs specified in this MPLS-TP OAM
architecture framework document. Unless otherwise stated, all
references to domains, LSRs, MPLS Sections, LSP, pseudowires and MEs
in this Section are made in relation to those shown in Figure 3.
4.1. MPLS-TP Section Monitoring
An MPLS-TP Section ME (SME) is an MPLS-TP maintenance entity intended
to monitor the forwarding behaviour of an MPLS Section as defined in
[10]. An SME may be configured on any MPLS section. SME OAM packets
fate share with the user data packets sent over the monitored MPLS
Section.
Busi et al. Expires January 13, 2010 [Page 15]
Internet-Draft MPLS-TP OAM Framework July 2009
[Editor's note - Is OAM monitoring only the forwarding behaviour? If
not, we need to clarify what it is monitoring]
An SME is intended to be deployed for applications where it is
preferable to monitor the link between topologically adjacent (next
hop in this layer network) MPLS (and MPLS-TP enabled) LSRs rather
than monitoring the individual LSP or PW segments traversing the MPLS
Section and the server layer technology does not provide adequate OAM
capabilities.
|<------------------- MS-PW1Z ------------------->|
| |
| |<-PSN13->| |<-PSN3X->| |<-PSNXZ->| |
V V LSP V V LSP V V LSP V V
+----+ +-+ +----+ +----+ +-+ +----+
+----+ |TPE1| | | |SPE3| |SPEX| | | |TPEZ| +----+
| | AC1 | |=========| |=========| |=========| | AC2 | |
| CE1|--------|........PW13.......|...PW3X..|.......PWXZ........|-------|CE2 |
| | | |=========| |=========| |=========| | | |
+----+ | 1 | |2| | 3 | | X | |Y| | Z | +----+
+----+ +-+ +----+ +----+ +-+ +----+
.--. .--. .--------. .--. .--.
Sec12 Sec23 Sec3X SecXY SecYZ
SME SME SME SME SME
Figure 4 Reference Example of MPLS-TP Section MEs (SME)
Figure 4 shows 5 Section MEs configured in the path between AC1 and
AC2: 1) Sec12 ME associated with the MPLS Section between LSR 1 and
LSR 2, 2) Sec23 ME associated with the MPLS Section between LSR 2 and
LSR 3, 3) Sec3X ME associated with the MPLS Section between LSR 3 and
LSR X, 4) SecXY ME associated with the MPLS Section between LSR X and
LSR Y, and 5) SecYZ ME associated with the MPLS Section between LSR Y
and LSR Z.
4.2. MPLS-TP LSP End-to-End Monitoring
An MPLS-TP LSP ME (LME) is an MPLS-TP maintenance entity intended to
monitor the forwarding behaviour of an end-to-end LSP between two
(e.g., a point-to-point LSP) or more (e.g., a point-to-multipoint
LSP) LERs. An LME may be configured on any MPLS LSP. LME OAM packets
fate share with user data packets sent over the monitored MPLS-TP
LSP.
Busi et al. Expires January 13, 2010 [Page 16]
Internet-Draft MPLS-TP OAM Framework July 2009
An LME is intended to be deployed in scenarios where it is desirable
to monitor the forwarding behaviour of an entire LSP between its
LERs, rather than, say, monitoring individual PWs.
|<------------------- MS-PW1Z ------------------->|
| |
| |<-PSN13->| |<-PSN3X->| |<-PSNXZ->| |
V V LSP V V LSP V V LSP V V
+----+ +-+ +----+ +----+ +-+ +----+
+----+ |TPE1| | | |SPE3| |SPEX| | | |TPEZ| +----+
| | AC1 | |=========| |=========| |=========| | AC2 | |
| CE1|--------|........PW13.......|...PW3X..|........PWXZ.......|-------|CE2 |
| | | |=========| |=========| |=========| | | |
+----+ | 1 | |2| | 3 | | X | |Y| | Z | +----+
+----+ +-+ +----+ +----+ +-+ +----+
.---------. .---------.
PSN13 LME PSNXZ LME
Figure 5 Examples of MPLS-TP LSP MEs (LME)
Figure 5 depicts 2 LMEs configured in the path between AC1 and AC2:
1) the PSN13 LME between LER 1 and LER 3, and 2) the PSNXZ LME
between LER X and LER Y. Note that the presence of a PSN3X LME in
such a configuration is optional, hence, not precluded by this
framework. For instance, the SPs may prefer to monitor the MPLS-TP
Section between the two LSRs rather than the individual LSPs.
4.3. MPLS-TP LSP Tandem Connection Monitoring
An MPLS-TP LSP Tandem Connection Monitoring ME (LTCME) is an MPLS-TP
maintenance entity intended to monitor the forwarding behaviour of an
arbitrary part of an LSP between a given pair of LSRs independently
from the end-to-end monitoring (LME). An LTCME can monitor an LSP
segment or concatenated segment and it may also include the
forwarding engine(s) of the node(s) at the edge(s) of the segment or
concatenated segment.
Multiple LTCMEs MAY be configured on any LSP. The LSRs that terminate
the LTCME may or may not be immediately adjacent at the MPLS-TP
layer. LTCME OAM packets fate share with the user data packets sent
over the monitored LSP segment.
A LTCME can be defined between the following entities:
o LER and any LSR of a given LSP.
Busi et al. Expires January 13, 2010 [Page 17]
Internet-Draft MPLS-TP OAM Framework July 2009
o Any two LSRs of a given LSP.
An LTCME is intended to be deployed in scenarios where it is
preferable to monitor the behaviour of a part of an LSP rather than
the entire LSP itself, for example when there is a need to monitor a
part of an LSP that extends beyond the administrative boundaries of
an MPLS-TP enabled administrative domain.
Note that LTCMEs are equally applicable to hierarchical LSPs.
|<--------------------- PW1Z -------------------->|
| |
| |<--------------PSN1Z LSP-------------->| |
| |<-PSN13->| |<-PSN3X->| |<-PSNXZ->| |
V V S-LSP V V S-LSP V V S-LSP V V
+----+ +-+ +----+ +----+ +-+ +----+
+----+ | PE1| | | |DBN3| |DBNX| | | | PEZ| +----+
| | AC1 | |=======================================| | AC2 | |
| CE1|--------|......................PW1Z.......................|-------|CE2 |
| | | |=======================================| | | |
+----+ | 1 | |2| | 3 | | X | |Y| | Z | +----+
+----+ +-+ +----+ +----+ +-+ +----+
. . . .
| | | |
|<---- Domain 1 --->| |<---- Domain Z --->|
.---------. .---------.
PSN13 LTCME PSNXZ LTCME
.---------------------------------------.
PSN1Z LME
DBN: Domain Border Node
Figure 6 MPLS-TP LSP Tandem Connection Monitoring ME (LTCME)
Figure 6 depicts a variation of the reference model in Figure 3 where
there is an end-to-end PSN LSP (PSN1Z LSP) between PE1 and PEZ. PSN1Z
LSP consists of, at least, three stitched LSP Segments: PSN13, PSN3X
and PSNXZ. In this scenario there are two separate LTCMEs configured
to monitor the forwarding behaviour of the PSN1Z LSP: 1) a LTCME
monitoring the PSN13 LSP Segment on Domain 1 (PSN13 LTCME), and 2) a
LTCME monitoring the PSNXZ LSP Segment on Domain Z (PSNXZ LTCME).
It is worth noticing that LTCMEs can coexist with the LME monitoring
the end-to-end LSP and that LTCME MEPs and LME MEPs can be coincident
Busi et al. Expires January 13, 2010 [Page 18]
Internet-Draft MPLS-TP OAM Framework July 2009
in the same node (e.g. PE1 node supports both the PSN1Z LME MEP and
the PSN13 LTCME MEP).
4.4. MPLS-TP PW Monitoring
An MPLS-TP PW ME (PME) is an MPLS-TP maintenance entity intended to
monitor the end-to-end forwarding behaviour of a SS-PW or MS-PW
between a pair of T-PEs. A PME MAY be configured on any SS-PW or MS-
PW. PME OAM packets fate share with the user data packets sent over
the monitored PW.
A PME is intended to be deployed in scenarios where it is desirable
to monitor the forwarding behaviour of an entire PW between a pair of
MPLS-TP enabled T-PEs rather than monitoring the LSP aggregating
multiple PWs between PEs.
|<------------------- MS-PW1Z ------------------->|
| |
| |<-PSN13->| |<-PSN3X->| |<-PSNXZ->| |
V V LSP V V LSP V V LSP V V
+----+ +-+ +----+ +----+ +-+ +----+
+----+ |TPE1| | | |SPE3| |SPEX| | | |TPEZ| +----+
| | AC1 | |=========| |=========| |=========| | AC2 | |
| CE1|--------|........PW13.......|...PW3X..|........PWXZ.......|-------|CE2 |
| | | |=========| |=========| |=========| | | |
+----+ | 1 | |2| | 3 | | X | |Y| | Z | +----+
+----+ +-+ +----+ +----+ +-+ +----+
.---------------------PW1Z PME--------------------.
Figure 7 MPLS-TP PW ME (PME)
Figure 7 depicts a MS-PW (MS-PW1Z) consisting of three segments:
PW13, PW3X and PWXZ and its associated end-to-end PME (PW1Z PME).
4.5. MPLS-TP MS-PW Tandem Connection Monitoring
An MPLS-TP MS-PW Tandem Connection Monitoring ME (PTCME) is an MPLS-
TP maintenance entity intended to monitor the forwarding behaviour of
an arbitrary part of an MS-PW between a given pair of PEs
independently from the end-to-end monitoring (PME). An PTCME can
monitor a PW segment or concatenated segment and it may alos include
the forwarding engine(s) of the node(s) at the edge(s) of the segment
or concatenated segment.
Multiple PTCMEs MAY be configured on any MS-PW. The PEs may or may
not be immediately adjacent at the MS-PW layer. PTCME OAM packets
Busi et al. Expires January 13, 2010 [Page 19]
Internet-Draft MPLS-TP OAM Framework July 2009
fate share with the user data packets sent over the monitored PW
Segment.
A PTCME can be defined between the following entities:
o T-PE and any S-PE of a given MS-PW
o Any two S-PEs of a given MS-PW. It can span several PW segments.
A PTCME is intended to be deployed in scenarios where it is
preferable to monitor the behaviour of a part of a MS-PW rather than
the entire end-to-end PW itself, for example to monitor an MS-PW
Segment within a given network domain of an inter-domain MS-PW.
|<------------------- MS-PW1Z ------------------->|
| |
| |<-PSN13->| |<-PSN3X->| |<-PSNXZ->| |
V V LSP V V LSP V V LSP V V
+----+ +-+ +----+ +----+ +-+ +----+
+----+ |TPE1| | | |SPE3| |SPEX| | | |TPEZ| +----+
| | AC1 | |=========| |=========| |=========| | AC2 | |
| CE1|--------|........PW13.......|...PW3X..|........PWXZ.......|-------|CE2 |
| | | |=========| |=========| |=========| | | |
+----+ | 1 | |2| | 3 | | X | |Y| | Z | +----+
+----+ +-+ +----+ +----+ +-+ +----+
.---- PW1 PTCME ----. .---- PW5 PTCME ----.
.---------------------PW1Z PME--------------------.
Figure 8 MPLS-TP MS-PW Tandem Connection Monitoring (PTCME)
Figure 8 depicts the same MS-PW (MS-PW1Z) between AC1 and AC2 as in
Figure 7. In this scenario there are two separate PTCMEs configured
to monitor the forwarding behaviour of MS-PW1Z: 1) a PTCME monitoring
the PW13 MS-PW Segment on Domain 1 (PW13 PTCME), and 2) a PTCME
monitoring the PWXZ MS-PW Segment on Domain Z with (PWXZ PTCME).
It is worth noticing that PTCMEs can coexist with the PME monitoring
the end-to-end MS-PW and that PTCME MEPs and PME MEPs can be
coincident in the same node (e.g. TPE1 node supports both the PW1Z
PME MEP and the PW13 PTCME MEP).
Busi et al. Expires January 13, 2010 [Page 20]
Internet-Draft MPLS-TP OAM Framework July 2009
5. OAM Functions for pro-active monitoring
5.1. Continuity Check and Connectivity Verification
[Editor's note - There is a need to decide whether pro-active CC and
CV functions need to be combined in the same tool or separated into
different tools. This version of the document combines the two
functions. Future versions will be aligned with the decision taken
about whether to combine or not CC and CV.]
Proactive Continuity Check and Connectivity Verification (CC-V)
functions are used to detect a loss of continuity (LOC), an
unexpected connectivity between two MEs (e.g. mismerging or
misconnection), as well as unexpected connectivity within the ME with
an unexpected MEP.
Execution of proactive CC-V is based on the (proactive) generation of
CC-V OAM packets by the source MEP that are processed by the sink
MEP. Each CC-V OAM packet MUST include a globally unique ME
identifier, and MUST be transmitted at a regular, operator's
configurable, rate. The default CC-V transmission periods are
application dependent (see section 5.1.4).
Proactive CC-V OAM packets are transmitted with the "minimum loss
probability PHB" within a single network operator. This PHB is
configurable on network operator's basis. PHBs can be translated at
the network borders.
[Editor's note - Describe the relation between the previous paragraph
and the fate sharing requirement. Need to clarify also in the
requirement document that for proactive CC-V the fate sharing is
related to the forwarding behavior and not to the QoS behavior]
In a bidirectional point-to-point transport path, when a MEP is
enabled to generate pro-active CC-V OAM packets with a configured
transmission rate, it also expects to receive pro-active CC-V OAM
packets from its peer MEP at the same transmission rate. In a
unidirectional transport path (either point-to-point or point-to-
multipoint), only the source MEP is enabled to generate CC-V OAM
packets and only the sink MEP is configured to expect these packets
at the configured rate.
MIPs, as well as intermediate nodes not supporting MPLS-TP OAM, are
transparent to the pro-active CC-V information and forward these pro-
active CC-V OAM packets as regular data packets.
Busi et al. Expires January 13, 2010 [Page 21]
Internet-Draft MPLS-TP OAM Framework July 2009
To initialize the proactive CC-V monitoring on a configured ME
without affecting traffic, the MEP source function (generating pro-
active CC-V packets) should be enabled prior to the corresponding MEP
sink function (detecting continuity and connectivity defects). When
disabling the CC-V proactive functionality, the MEP sink function
should be disabled prior to the corresponding MEP source function.
5.1.1. Defects identified by CC-V
Pro-active CC-V functions allow a sink MEP to detect the following
defect conditions.
For all of these defect cases, the sink MEP SHOULD notify the
equipment fault management process of the detected defect.
[Editor's note - Investigate whether in case there is a
misconfiguration on the minimum loss probability PHB on the two MEPs
a defect can be useful to notify the misconfiguration to the
operator.]
5.1.1.1. Loss Of Continuity defect
When proactive CC-V is enabled, a sink MEP detects a loss of
continuity (LOC) defect when it fails to receive pro-active CC-V OAM
packets from the peer MEP.
o Entry criteria: if no pro-active CC-V OAM packets from the peer
MEP (i.e. with the correct ME and peer MEP identifiers) are
received within the interval equal to 3.5 times the receiving
MEP's configured CC-V transmission period.
o Exit criteria: a pro-active CC-V OAM packet from the peer MEP
(i.e. with the correct ME and peer MEP identifiers) is received.
5.1.1.2. Mis-connectivity defect
When a pro-active CC-V OAM packet is received, a sink MEP identifies
a mis-connectivity defect (e.g. mismerge or misconnection) with its
peer source MEP when the received packet carries an incorrect ME
identifier.
o Entry criteria: the sink MEP receives a pro-active CC-V OAM packet
with an incorrect ME ID.
Busi et al. Expires January 13, 2010 [Page 22]
Internet-Draft MPLS-TP OAM Framework July 2009
o Exit criteria: the sink MEP does not receive any pro-active CC-V
OAM packet with an incorrect ME ID for an interval equal at least
to 3.5 times the longest transmission period of the pro-active
CC-V OAM packets received with an incorrect ME ID since this
defect has been raised.
5.1.1.3. MEP misconfiguration defect
When a pro-active CC-V packet is received, a sink MEP identifies a
MEP misconfiguration defect with its peer source MEP when the
received packet carries a correct ME Identifier but an unexpected
peer MEP Identifier which includes the MEP's own MEP Identifier.
o Entry criteria: the sink MEP receives a CC-V pro-active packet
with correct ME ID but with unexpected MEP ID.
o Exit criteria: the sink MEP does not receive any pro-active CC-V
OAM packet with a correct ME ID and unexpected MEP ID for an
interval equal at least to 3.5 times the longest transmission
period of the pro-active CC-V OAM packets received with a correct
ME ID and unexpected MEP ID since this defect has been raised.
5.1.1.4. Period Misconfiguration defect
If pro-active CC-V OAM packets is received with a correct ME and MEP
identifiers but with a transmission period different than its own
configured transmission period, then a CC-V period mis-configuration
defect is detected
o Entry criteria: a MEP receives a CC-V pro-active packet with
correct ME ID and MEP ID but with a Period field value different
than its own CC-V configured transmission period.
o Exit criteria: the sink MEP does not receive any pro-active CC-V
OAM packet with a correct ME and MEP IDs and an incorrect
transmission period for an interval equal at least to 3.5 times
the longest transmission period of the pro-active CC-V OAM packets
received with a correct ME and MEP IDs and an incorrect
transmission period since this defect has been raised.
5.1.2. Consequent action
A sink MEP that detects one of the defect conditions defined in
section 5.1.1 MUST perform the following consequent actions. Some of
these consequent actions SHOULD be enabled/disabled by the operator
depending upon the application used (see section 5.1.4).
Busi et al. Expires January 13, 2010 [Page 23]
Internet-Draft MPLS-TP OAM Framework July 2009
If a MEP detects an unexpected ME Identifier, or an unexpected MEP,
it MUST block all the traffic (including also the user data packets)
that it receives from the misconnected transport path.
If a MEP detects LOC defect and the CC-V monitoring is enabled it
SHOULD block all the traffic (including also the user data packets)
that it receives from the transport path if this consequent action
has been enabled by the operator.
It is worth noticing that the OAM requirements document [11]
recommends that CC-V proactive monitoring is enabled on every ME in
order to reliably detect connectivity defects. However, CC-V
proactive monitoring MAY be disabled by an operator on a ME. In the
event of a misconnection between a transport path that is pro-
actively monitored for CC-V and a transport path which is not, the
MEP of the former transport path will detect a LOC defect
representing a connectivity problem (e.g. a misconnection with a
transport path where CC-V proactive monitoring is not enabled)
instead of a continuity problem, with a consequent wrong traffic
delivering. For these reasons, the traffic block consequent action is
applied even when a LOC condition occurs. This block consequent
action MAY be disabled through configuration. This deactivation of
the block action, may be used for activating or deactivating the
monitoring when it is not possible to synchronize the function
activation of the two peer MEPs.
If a MEP detects a LOC defect, an unexpected ME Identifier, or an
unexpected MEP it MUST declare a signal fail condition at the
transport path level.
If a MEP detects an Unexpected Period defect it SHOULD declare a
signal fail condition at the transport path level.
[Editor's note - Transport equipment also performs defect correlation
(as defined in G.806) in order to properly report failures to the
transport NSM. The current working assumption, to be further
investigated, is that defect correlations are outside the scope of
this document and to be defined in ITU-T documents.]
5.1.3. Configuration considerations
At all MEPs inside a ME, the following configuration information need
to be configured when pro-active CC-V function is enabled:
o ME ID; the ME identifier to which the MEP belongs;
o MEP-ID; the MEP's own identity inside the ME;
Busi et al. Expires January 13, 2010 [Page 24]
Internet-Draft MPLS-TP OAM Framework July 2009
o list of peer MEPs inside the ME. For a point-to-point ME the list
would consist of the single peer MEP ID from which the OAM packets
are expected. In case of the root MEP of a p2mp ME, the list is
composed by all the leaf MEP IDs inside the ME. In case of the
leaf MEP of a p2mp ME, the list is composed by the root MEP ID
(i.e. each leaf MUST know the root MEP ID from which it expect to
receive the CC-V OAM packets).
o transmission rate; the default CC-V transmission periods are
application dependent (see section 5.1.4)
o PHB; it identifies the per-hop behaviour of CC-V packet. Proactive
CC-V packets are transmitted with the "minimum loss probability
PHB" previously configured within a single network operator. This
PHB is configurable on network operator's basis. PHBs can be
translated at the network borders.
For statically provisioned transport paths the above information are
statically configured; for dynamically established transport paths
the configuration information are signaled via the control plane.
5.1.4. Applications for proactive CC-V
CC-V is applicable for fault management, performance monitoring, or
protection switching applications.
o Fault Management: default transmission period is 1s (i.e.
transmission rate of 1 packet/second)
o Performance Monitoring: default transmission period is 100ms (i.e.
transmission rate of 10 packets/second)
o Protection Switching: in order to achieve sub-50ms recovery time
the default transmission period is 3.33ms (i.e. transmission rate
of 300 packets/second) although a transmission period of 10ms can
also be used. In some cases, when a slower recovery time is
acceptable, it is also possible to lengthen the transmission rate.
It SHOULD be possible for the operator to configure these
transmission rates for all applications, to satisfy his internal
requirements.
In addition, the operator should be able to define the consequent
action to be performed for each of these applications.
Busi et al. Expires January 13, 2010 [Page 25]
Internet-Draft MPLS-TP OAM Framework July 2009
5.2. Remote Defect Indication
The Remote Defect Indication (RDI) is an indicator that is
transmitted by a MEP to communicate to its peer MEPs that a signal
fail condition exists. RDI is only used for bidirectional
connections and is associated with proactive CC-V activation. The RDI
indicator is piggy-backed onto the CC-V packet.
When a MEP detects a signal fail condition (e.g. in case of a
continuity or connectivity defect or an AIS condition is detected),
it should begin transmitting an RDI indicator to its peer MEP. The
RDI information will be included in all pro-active CC-V packets that
it generates for the duration of the signal fail condition's
existence.
[Editor's note - Add some forward compatibility information to cover
the case where future OAM mechanisms that contributes to the signal
fail detection (and RDI generation) are defined.]
A MEP that receives the packets with the RDI information should
determine that its peer MEP has encountered a defect condition
associated with a signal fail.
MIPs as well as intermediate nodes not supporting MPLS-TP OAM are
transparent to the RDI indicator and forward these proactive CC-V
packets that include the RDI indicator as regular data packets, i.e.
the MIP should not perform any actions nor examine the indicator.
When the signal fail defect condition clears, the MEP should clear
the RDI indicator from subsequent transmission of pro-active CC-V
packets. A MEP should clear the RDI defect upon reception of a pro-
active CC-V packet from the source MEP with the RDI indicator
cleared.
5.2.1. Configuration considerations
In order to support RDI indication, the RDI transmission rate and PHB
of the MEP should be configured as part of the CC-V configuration.
5.2.2. Applications for Remote Defect Indication
RDI is applicable for the following applications:
Busi et al. Expires January 13, 2010 [Page 26]
Internet-Draft MPLS-TP OAM Framework July 2009
o Single-ended fault management - A MEP that receives an RDI
indication from its peer MEP, can report a far-end defect
condition (i.e. the peer MEP has detected a signal fail condition
in the traffic direction from the MEP that receives the RDI
indication to the peer MEP that has sent the RDI information).
o Contribution to far-end performance monitoring - The indication of
the far-end defect condition is used as a contribution to the
bidirectional performance monitoring process.
5.3. Alarm Reporting
Alarm Reporting function relies upon an Alarm Indication Signal (AIS)
message used to suppress alarms following detection of defect
conditions at the server (sub) layer.
o A server MEP that detects a signal fail conditions in the server
(sub-)layer, can generate packets with AIS information in a
direction opposite to its peers MEPs to allow the suppression of
secondary alarms at the MEP in the client (sub-)layer.
A server MEP is responsible for notifying the MPLS-TP layer network
MEP upon fault detection in the server layer network to which the
server MEP is associated.
Only Server MEPs can issue MPLS-TP packets with AIS information. Upon
detection of a signal fail condition the Server MEP can immediately
start transmitting periodic packets with AIS information. These
periodic packets, with AIS information, continue to be transmitted
until the signal fail condition is cleared.
Upon receiving a packet with AIS information an MPLS-TP MEP detects
an AIS defect condition and suppresses loss of continuity alarms
associated with all its peer MEPs. A MEP resumes loss of continuity
alarm generation upon detecting loss of continuity defect conditions
in the absence of AIS condition.
Busi et al. Expires January 13, 2010 [Page 27]
Internet-Draft MPLS-TP OAM Framework July 2009
For example, let's consider a fiber cut between LSR 1 and LSR 2 in
the reference network of Figure 3. Assuming that all the MEs
described in Figure 3 have pro-active CC-V enabled, a LOC defect is
detected by the MEPs of Sec12 SME, PSN13 LME, PW1 PTCME and PW1Z PME,
however in transport network only the alarm associate to the fiber
cut needs to be reported to NMS while all these secondary alarms
should be suppressed (i.e. not reported to the NMS or reported as
secondary alarms).
If the fiber cut is detected by the MEP in the physical layer (in
LSR2), LSR2 can generate the proper alarm in the physical layer and
suppress the secondary alarm associated with the LOC defect detected
on Sec12 SME. As both MEPs reside within the same node, this process
does not involve any external protocol exchange. Otherwise, if the
physical layer has not enough OAM capabilities to detect the fiber
cut, the MEP of Sec12 SME in LSR2 will report a LOC alarm.
In both cases, the MEP of Sec12 SME in LSR 2 generates AIS packets on
the PSN13 LME in order to allow its MEP in LSR3 to suppress the LOC
alarm.
LSR3 can also suppress the secondary alarm on PW1 PTCME because the
MEP of PW1 PTCME resides within the same node as the MEP of PSN13
LME.
The MEP of PW1 PTCME in LSR3 also generates AIS packets on PW1Z PME
in order to allow its MEP in LSRZ to suppress the LOC alarm.
The generation of AIS packets for each MEs in the client (sub-)layer
is configurable (i.e. the operator can enable/disable the AIS
generation).
AIS packets are transmitted with the "minimum loss probability PHB"
within a single network operator. This PHB is configurable on network
operator's basis.
A MIP is transparent to packets with AIS information and therefore
does not require any information to support AIS functionality.
5.4. Lock Reporting
[Editor's note - Requirements for Lock Indication and Lock Reporting
are still under discussion in draft-ietf-mpls-tp-oam-requirement-02.
Lock Indication is not required by draft-ietf-mpls-tp-oam-
requirement-02 This section will be aligned according to the final
decision regarding the requirement.]
Busi et al. Expires January 13, 2010 [Page 28]
Internet-Draft MPLS-TP OAM Framework July 2009
To be incorporated in a future revision of this document
5.5. Lock Indication
[Editor's note - Requirements for Lock Indication and Lock Reporting
are still under discussion in draft-ietf-mpls-tp-oam-requirement-02.
Lock Indication is not required by draft-ietf-mpls-tp-oam-
requirement-02 This section will be aligned according to the final
decision regarding the requirement.]
The Locked Indication Signal (LIS) is used to propagate an
administrative locking of a source MEP and consequential interruption
of data forwarding towards the sink MEP. It allows a sink MEP
receiving LIS to differentiate between a defect condition and an
administrative locking action at the source MEP. An example
application that requires administrative locking of a MEP is the out-
of-service test.
5.6. Packet Loss
Packet Loss (LM) is one of the capabilities supported by the MPLS-TP
Performance Monitoring (PM) function in order to facilitate reporting
of QoS information for a transport path. LM is used to exchange
counter values for the number of ingress and egress packets
transmitted and received by the transport path monitored by a pair of
MEPs.
Pro-active LM is performed by periodically sending LM OAM packets
from a MEP to a peer MEP and by receiving LM OAM packets from the
peer MEP (if a bidirectional transport path) during the life time of
the transport path. Each MEP performs measurements of its transmitted
and received packets. These measurements are then correlated to
derive the impact of packet loss on a number of performance metrics
for the transport path.
For a MEP, near-end packet loss refers to packet loss associated with
incoming data packets (from the far-end MEP) while far-end packet
loss refers to packet loss associated with egress data packets
(towards the far-end MEP).
5.6.1. Configuration considerations
In order to support pro-active LM, the transmission rate and PHB
associated with the LM OAM packets originating from a MEP need be
configured as part of the LM provisioning procedures. LM OAM packets
should be transmitted with the PHB that yields the lowest packet loss
Busi et al. Expires January 13, 2010 [Page 29]
Internet-Draft MPLS-TP OAM Framework July 2009
performance among the PHB Scheduling Classes or Ordered Aggregates
(see RFC 3260 [14]) in the monitored transport path for the relevant
network domain(s).
5.6.2. Applications for Packet Loss
LM is relevant for the following applications:
o Single or double-end performance monitoring: determination of the
packet loss performance of a transport path for SLS verification
purposes.
o Single or double-end performance monitoring: determination of the
packet loss performance of a PHB Scheduling Class or Ordered
Aggregate within a transport path
o Contribution to service unable time. Both near-end and far-end
packet loss measurements contribute to performance metrics such as
near-end severely errored seconds (Near-End SES) and far-end
severely errored seconds (Far-End SES) respectively, which
together contribute to unavailable time, in a manner similar to
Recommendation G.826 [19] and Recommendation G.7710 [20].
5.7. Client Failure Indication
The Client Failure Indication (CSF) function is used to help process
client defects and propagate a client signal defect condition from
the process associated with the local attachment circuit where the
defect was detected (typically the source adaptation function for the
local client interface) to the process associated with the far-end
attachment circuit (typically the source adaptation function for the
far-end client interface) for the same transmission path in case the
client of the transmission path does not support a native
defect/alarm indication mechanism, e.g. FDI/AIS.
A source MEP starts transmitting a CSF indication to its peer MEP
when it receives a local client signal defect notification via its
local CSF function. Mechanisms to detect local client signal fail
defects are technology specific.
A sink MEP that has received a CSF indication report this condition
to its associated client process via its local CSF function.
Consequent actions toward the client attachment circuit are
technology specific.
Busi et al. Expires January 13, 2010 [Page 30]
Internet-Draft MPLS-TP OAM Framework July 2009
5.7.1. Configuration considerations
In order to support RCSF indication, the CSF transmission rate and
PHB of the CSF OAM packet should be configured as part of the CSF
configuration.
5.7.2. Applications for Remote Defect Indication
CSF is applicable for the following applications:
o Single-ended fault management - A MEP that receives a CSF
indication from its peer MEP, can report a far-end client defect
condition (i.e. the peer MEP has been informed of local client
signal fail condition in the traffic direction from the client to
the peer MEP that transmitted the CSF).
o Contribution to far-end performance monitoring - The indication of
the far-end defect condition may be used to account on network
operator contribution to the bidirectional performance monitoring
process.
CSF supports the application described in Appendix VIII of ITU-T
G.806 [18].
5.8. Delay Measurement
Delay Measurement (DM) is one of the capabilities supported by the
MPLS-TP PM function in order to facilitate reporting of QoS
information for a transport path. Specifically, pro-active DM is used
to measure the long-term packet delay and packet delay variation in
the transport path monitored by a pair of MEPs.
Pro-active DM is performed by sending periodic DM OAM packets from a
MEP to a peer MEP and by receiving DM OAM packets from the peer MEP
(if a bidirectional transport path) during a configurable time
interval.
Pro-active DM can be operated in two ways:
o One-way: a MEP sends DM OAM packet to its peer MEP containing all
the required information to facilitate one-way packet delay and/or
one-way packet delay variation measurements at the peer MEP.
Busi et al. Expires January 13, 2010 [Page 31]
Internet-Draft MPLS-TP OAM Framework July 2009
o Two-way: a MEP sends DM OAM packet with a DM request to its peer
MEP, which replies with an DM OAM packet as a DM response. The
request/response DM OAM packets containing all the required
information to facilitate two-way packet delay and/or two-way
packet delay variation measurements from the viewpoint of the
source MEP.
5.8.1. Configuration considerations
In order to support pro-active DM, the transmission rate and PHB
associated with the DM OAM packets originating from a MEP need be
configured as part of the LM provisioning procedures. DM OAM packets
should be transmitted with the PHB that yields the lowest packet loss
performance among the PHB Scheduling Classes or Ordered Aggregates
(see RFC 3260 [14]) in the monitored transport path for the relevant
network domain(s).
5.8.2. Applications for Packet Loss
DM is relevant for the following applications:
o Single or double-end performance monitoring: determination of the
delay performance of a transport path for SLS verification
purposes.
o Single or double-end performance monitoring: determination of the
delay performance of a PHB Scheduling Class or Ordered Aggregate
within a transport path
6. OAM Functions for on-demand monitoring
6.1. Connectivity Verification
In order to preserve network resources, e.g. bandwidth, processing
time at switches, it may be preferable to not use pro-active CC-V.
In order to perform fault management functions network management may
invoke periodic on-demand bursts of on-demand CV packets. Use of on-
demand CV is dependent on the existence of a bi-directional
connection ME, because it requires the presence of a return path in
the data plane.
[Editor's note - Clarify in the sentence above and within the
paragraph that on-demand CV requires a return path to send back the
reply to on-demand CV packets]
An additional use of on-demand CV would be to detect and locate a
problem of connectivity when a problem is suspected or known based on
Busi et al. Expires January 13, 2010 [Page 32]
Internet-Draft MPLS-TP OAM Framework July 2009
other tools. In this case the functionality will be triggered by the
network management in response to a status signal or alarm
indication.
On-demand CV is based upon generation of on-demand CV packets that
should uniquely identify the ME that is being checked. The on-demand
functionality may be used to check either an entire ME (end-to-end)
or between a MEP to a specific MIP.
On-demand CV may generate a one-time burst of on-demand CV packets,
or be used to invoke periodic, non-continuous, bursts of on-demand CV
packets. The number of packets generated in each burst is
configurable at the MEPs, and should take into account normal packet-
loss conditions.
When invoking a periodic check of the ME, the source MEP should issue
a burst of on-demand CV packets that uniquely identifies the ME being
verified. The number of packets and their transmission rate should
be pre-configured and known to both the source MEP and the target MEP
or MIP. The source MEP should use the TTL field to indicate the
number of hops necessary, when targeting a MIP and use the default
value when performing an end-to-end check [IB => This is quite
generic for addressing packets to MIPs and MEPs so it is better to
move this text in section 2]. The target MEP/MIP shall return a
reply on-demand CV packet for each packet received. If the expected
number of on-demand CV reply packets is not received at source MEP, a
LOC state is detected.
[Editor's note - We need to add some text for the usage of on-demand
CV with different packet sizes, e.g. to discover MTU problems.]
When a connectivity problem is detected (e.g. via a pro-active CC-V
OAM tool), on demand CV tool can be used to check the path. The
series should check CV from MEP to peer MEP on the path, and if a
fault is discovered, by lack of response, then additional checks may
be performed to each of the intermediate MIP to locate the fault.
6.1.1. Configuration considerations
For on-demand CV the MEP should support configuration of number of
packets to be transmitted/received in each burst of transmissions and
their packet size. The transmission rate should be either pre-
configured or negotiated between the different nodes.
In addition, when the CV packet is used to check connectivity toward
a target MIP, the number of hops to reach the target MIP should be
configured.
Busi et al. Expires January 13, 2010 [Page 33]
Internet-Draft MPLS-TP OAM Framework July 2009
The PHB of the on-demand CV packets should be configured as well.
[Editor's note - We need to be better define the reason for such
configuration]
6.2. Packet Loss
On-demand Packet Loss (LM) is one of the capabilities supported by
the MPLS-TP Performance Monitoring function in order to facilitate
diagnostic of QoS performance for a transport path. As Pro-active LM,
on-demand LM is used to exchange counter values for the number of
ingress and egress packets transmitted and received by the transport
path monitored by a pair of MEPs.
On-demand LM is performed by periodically sending LM OAM packets from
a MEP to a peer MEP and by receiving LM OAM packets from the peer MEP
(if a bidirectional transport path) during a pre-defined monitoring
period. Each MEP performs measurements of its transmitted and
received packets. These measurements are then correlated evaluate the
packet loss performance metrics of the transport path.
6.2.1. Configuration considerations
In order to support on-demand LM, the beginning and duration of the
LM procedures,the transmission rate and PHB associated with the LM
OAM packets originating from a MEP must be configured as part of the
on-demand LM provisioning procedures. LM OAM packets should be
transmitted with the PHB that yields the lowest packet loss
performance among the PHB Scheduling Classes or Ordered Aggregates
(see RFC 3260 [14]) in the monitored transport path for the relevant
network domain(s).
6.2.2. Applications for On-demand Packet Loss
On-demand LM is relevant for the following applications:
o Single-end performance monitoring: diagnostic of the packet loss
performance of a transport path for SLS trouble shooting purposes.
o Single-end performance monitoring: diagnostic of the packet loss
performance of a PHB Scheduling Class or Ordering Aggregate within
a transport path for QoS trouble shooting purposes.
6.3. Diagnostic
To be incorporated in a future revision of this document
Busi et al. Expires January 13, 2010 [Page 34]
Internet-Draft MPLS-TP OAM Framework July 2009
6.4. Route Tracing
To be incorporated in a future revision of this document
6.5. Delay Measurement
Delay Measurement (DM) is one of the capabilities supported by the
MPLS-TP PM function in order to facilitate reporting of QoS
information for a transport path. Specifically, on-demand DM is used
to measure packet delay and packet delay variation in the transport
path monitored by a pair of MEPs during a pre-defined monitoring
period.
On-Demand DM is performed by sending periodic DM OAM packets from a
MEP to a peer MEP and by receiving DM OAM packets from the peer MEP
(if a bidirectional transport path) during a configurable time
interval.
On-demand DM can be operated in two ways:
o One-way: a MEP sends DM OAM packet to its peer MEP containing all
the required information to facilitate one-way packet delay and/or
one-way packet delay variation measurements at the peer MEP.
o Two-way: a MEP sends DM OAM packet with a DM request to its peer
MEP, which replies with an DM OAM packet as a DM response. The
request/response DM OAM packets containing all the required
information to facilitate two-way packet delay and/or two-way
packet delay variation measurements from the viewpoint of the
source MEP.
6.5.1. Configuration considerations
In order to support on-demand DM, the beginning and duration of the
DM procedures, the transmission rate and PHB associated with the DM
OAM packets originating from a MEP need be configured as part of the
LM provisioning procedures. DM OAM packets should be transmitted with
the PHB that yields the lowest packet delay performance among the PHB
Scheduling Classes or Ordering Aggregates (see RFC 3260 [14]) in the
monitored transport path for the relevant network domain(s).
6.5.2. Applications for Delay Measurement
DM is relevant for the following applications:
Busi et al. Expires January 13, 2010 [Page 35]
Internet-Draft MPLS-TP OAM Framework July 2009
o Single or double-end performance monitoring: determination of the
packet delay and/or delay variation performance of a transport
path for SLS verification purposes.
o Single or double-end performance monitoring: determination of the
packet delay and/or delay variation a PHB Scheduling Class or
Ordering Aggregate within a transport path
o Contribution to service unable time. Packet delay measurements may
contribute to performance metrics such as near-end severely
errored seconds (Near-End SES) and far-end severely errored
seconds (Far-End SES), which together contribute to unavailable
time.
6.6. Lock Instruct
To be incorporated in a future revision of this document
7. Security Considerations
A number of security considerations important in the context of OAM
applications.
OAM traffic can reveal sensitive information such as passwords,
performance data and details about e.g. the network topology. The
nature of OAM data therefore suggests to have some form of
authentication, authorization and encryption in place. This will
prevent unauthorized access to vital equipment and it will prevent
third parties from learning about sensitive information about the
transport network.
Mechanisms that the framework does not specify might be subject to
additional security considerations.
8. IANA Considerations
No new IANA considerations.
9. Acknowledgments
The authors would like to thank all members of the teams (the Joint
Working Team, the MPLS Interoperability Design Team in IETF and the
T-MPLS Ad Hoc Group in ITU-T) involved in the definition and
specification of MPLS Transport Profile.
This document was prepared using 2-Word-v2.0.template.dot.
Busi et al. Expires January 13, 2010 [Page 36]
Internet-Draft MPLS-TP OAM Framework July 2009
10. References
10.1. Normative References
[1] Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", BCP 14, RFC 2119, March 1997
[2] Rosen, E., Viswanathan, A., Callon, R., "Multiprotocol Label
Switching Architecture", RFC 3031, January 2001
[3] Rosen, E., et al., "MPLS Label Stack Encoding", RFC 3032,
January 2001
[4] Agarwal, P., Akyol, B., "Time To Live (TTL) Processing in
Multi-Protocol Label Switching (MPLS) Networks", RFC 3443,
January 2003
[5] Bryant, S., Pate, P., "Pseudo Wire Emulation Edge-to-Edge
(PWE3) Architecture", RFC 3985, March 2005
[6] Nadeau, T., Pignataro, S., "Pseudowire Virtual Circuit
Connectivity Verification (VCCV): A Control Channel for
Pseudowires", RFC 5085, December 2007
[7] Bocci, M., Bryant, S., "An Architecture for Multi-Segment
Pseudo Wire Emulation Edge-to-Edge", draft-ietf-pwe3-ms-pw-
arch-05 (work in progress), September 2008
[8] Bocci, M., et al., "A Framework for MPLS in Transport
Networks", draft-ietf-mpls-tp-framework-01 (work in progress),
June 2009
[9] Vigoureux, M., Bocci, M., Swallow, G., Ward, D., Aggarwal, R.,
"MPLS Generic Associated Channel ", RFC 5586, June 2009
10.2. Informative References
[10] Niven-Jenkins, B., Brungard, D., Betts, M., sprecher, N., Ueno,
S., "MPLS-TP Requirements", draft-ietf-mpls-tp-requirements-09
(work in progress), June 2009
[11] Vigoureux, M., Betts, M., Ward, D., "Requirements for OAM in
MPLS Transport Networks", draft-ietf-mpls-tp-oam-requirements-
02 (work in progress), June 2009
Busi et al. Expires January 13, 2010 [Page 37]
Internet-Draft MPLS-TP OAM Framework July 2009
[12] Sprecher, N., Nadeau, T., van Helvoort, H., Weingarten, Y.,
"MPLS-TP OAM Analysis", draft-sprecher-mpls-tp-oam-analysis-04
(work in progress), May 2009
[13] Nichols, K., Blake, S., Baker, F., Black, D., "Definition of
the Differentiated Services Field (DS Field) in the IPv4 and
IPv6 Headers", RFC 2474, December 1998
[14] Grossman, D., "New terminology and clarifications for
Diffserv", RFC 3260, April 2002.
[15] Farrel, A., Ayyangar, A., Vasseur, JP., "Inter-Domain MPLS and
GMPLS Traffic Engineering -- Resource Reservation Protocol-
Traffic Engineering (RSVP-TE) Extensions", RFC 5151, February
2008
[16] ITU-T Recommendation G.707/Y.1322 (01/07), "Network node
interface for the synchronous digital hierarchy (SDH)", January
2007
[17] ITU-T Recommendation G.805 (03/00), "Generic functional
architecture of transport networks", March 2000
[18] ITU-T Recommendation G.806 (01/09), "Characteristics of
transport equipment - Description methodology and generic
functionality ", January 2009
[19] ITU-T Recommendation G.826 (12/02), "End-to-end error
performance parameters and objectives for international,
constant bit-rate digital paths and connections", December 2002
[20] ITU-T Recommendation G.7710 (07/07), "Common equipment
management function requirements", July 2007
[21] ITU-T Recommendation Y.2611 (06/12), " High-level architecture
of future packet-based networks", 2006
Authors' Addresses
Italo Busi (Editor)
Alcatel-Lucent
Email: Italo.Busi@alcatel-lucent.it
Busi et al. Expires January 13, 2010 [Page 38]
Internet-Draft MPLS-TP OAM Framework July 2009
Ben Niven-Jenkins (Editor)
BT
Email: benjamin.niven-jenkins@bt.com
Contributing Authors' Addresses
Annamaria Fulignoli
Ericsson
Email: annamaria.fulignoli@ericsson.com
Enrique Hernandez-Valencia
Alcatel-Lucent
Email: enrique@alcatel-lucent.com
Lieven Levrau
Alcatel-Lucent
Email: llevrau@alcatel-lucent.com
Dinesh Mohan
Nortel
Email: mohand@nortel.com
Vincenzo Sestito
Alcatel-Lucent
Email: vincenzo.sestito@alcatel-lucent.it
Nurit Sprecher
Nokia Siemens Networks
Email: nurit.sprecher@nsn.com
Busi et al. Expires January 13, 2010 [Page 39]
Internet-Draft MPLS-TP OAM Framework July 2009
Huub van Helvoort
Huawei Technologies
Email: hhelvoort@huawei.com
Martin Vigoureux
Alcatel-Lucent
Email: martin.vigoureux@alcatel-lucent.fr
Yaacov Weingarten
Nokia Siemens Networks
Email: yaacov.weingarten@nsn.com
Rolf Winter
NEC
Email: Rolf.Winter@nw.neclab.eu
Busi et al. Expires January 13, 2010 [Page 40]
